Theory and Practice of Transactional Method Caching

Nowadays, tiered architectures are widely accepted for constructing large scale information systems. In this context application servers often form the bottleneck for a system's efficiency. An application server exposes an object oriented interface consisting of set of methods which are accessed by potentially remote clients. The idea of method caching is to store results of read-only method invocations with respect to the application server's interface on the client side. If the client invokes the same method with the same arguments again, the corresponding result can be taken from the cache without contacting the server. It has been shown that this approach can considerably improve a real world system's efficiency. This paper extends the concept of method caching by addressing the case where clients wrap related method invocations in ACID transactions. Demarcating sequences of method calls in this way is supported by many important application server standards. In this context the paper presents an architecture, a theory and an efficient protocol for maintaining full transactional consistency and in particular serializability when using a method cache on the client side. In order to create a protocol for scheduling cached method results, the paper extends a classical transaction formalism. Based on this extension, a recovery protocol and an optimistic serializability protocol are derived. The latter one differs from traditional transactional cache protocols in many essential ways. An efficiency experiment validates the approach: Using the cache a system's performance and scalability are considerably improved

Method-based caching in multi-tiered server applications

Abstract In recent years, application server technology has become very popular for building complex but mission-critical systems such as Web-based E-Commerce applications. However, the resulting solutions tend to suffer from serious performance and scalability bottlenecks, because of their distributed nature and their various software layers. This paper deals with the problem by presenting an approach about transparently caching results of a service interface\u27s read-only methods on the client side. Cache consistency is provided by a descriptive cache invalidation model which may be specified by an application programmer. As the cache layer is transparent to the server as well as to the client code, it can be integrated with relatively low effort even in systems that have already been implemented. Experimental results show that the approach is very effective in improving a server\u27s response times and its transactional throughput. Roughly speaking, the overhead for cache maintenance is small when compared to the cost for method invocations on the server side. The cache\u27s performance improvements are dominated by the fraction of read method invocations and the cache hit rate. Our experiments are based on a realistic E-commerce Web site scenario and site user behaviour is emulated in an authentic way. By inserting our cache, the maximum user request throughput of the web application could be more than doubled while its response time (such as perceived by a web client) was kept at a very low level. Moreover, the cache can be smoothly integrated with traditional caching strategies acting on other system tiers (e.g. caching of dynamic Web pages on a Web server). The presented approach as well as the related implementation are not restricted to application server scenarios but may be applied to any kind of interface-based software layers

Database server workload characterization in an e-commerce environment

A typical E-commerce system that is deployed on the Internet has multiple layers that include Web users, Web servers, application servers, and a database server. As the system use and user request frequency increase, Web/application servers can be scaled up by replication. A load balancing proxy can be used to route user requests to individual machines that perform the same functionality. To address the increasing workload while avoiding replicating the database server, various dynamic caching policies have been proposed to reduce the database workload in E-commerce systems. However, the nature of the changes seen by the database server as a result of dynamic caching remains unknown. A good understanding of this change is fundamental for tuning a database server to get better performance. In this study, the TPC-W (a transactional Web E-commerce benchmark) workloads on a database server are characterized under two different dynamic caching mechanisms, which are generalized and implemented as query-result cache and table cache. The characterization focuses on response time, CPU computation, buffer pool references, disk I/O references, and workload classification. This thesis combines a variety of analysis techniques: simulation, real time measurement and data mining. The experimental results in this thesis reveal some interesting effects that the dynamic caching has on the database server workload characteristics. The main observations include: (a) dynamic cache can considerably reduce the CPU usage of the database server and the number of database page references when it is heavily loaded; (b) dynamic cache can also reduce the database reference locality, but to a smaller degree than that reported in file servers. The data classification results in this thesis show that with dynamic cache, the database server sees TPC-W profiles more like on-line transaction processing workloads

Mobile map client API : design and implementation for Android

The fast development of computational power of the mobile phone makes it a suitable platform for running map applications. Both public and field working professionals can benefit from easy access to a mobile map client application with features such as route planning, location based services and simple GIS operations. This master's thesis describes the mobile operating system (OS) Android from a geographic information aspect and relates it to other major mobile OS. Available map client application programming interfaces (API) are investigated. It is concluded that Android is a good platform choice for implementing mobile map applications. But there is need of a generic open source API for Android. Such an API is implemented, resulting in a good performing map client. Though it needs additional development to perform all features aimed for in the suggested API design.Populärvetenskaplig sammanfattning: Dagens datorlika mobiltelefoner lämpar sig utmärkt för att visa olika typer av kartor. Det är inte svårt att hitta tillämpningar för både privatpersoner och professionella användare med behov som att till exempel hitta lämpliga färdvägar eller visa information om platsen man befinner sig på. Det här examensarbetet går ut på att undersöka hur geografisk data kan behandlas och visas som kartor på Android-mobiler. Målet är att skapa ett generellt programmeringsverktyg som ska kunna användas för att snabbt och enkelt kunna utveckla specialiserade kartapplikationer för Android. Ett sådant verktyg kallas inom databranschen för API, vilket står för Application Programming Interface. Ett API är ett gränssnitt som ger programmerare smidig tillgång till grundläggande funktioner i ett system eller en typ av applikation. I det här fallet får programmeraren tillgång till grundläggande kartfunktioner, som t.ex. kartdataladdning eller panorering och zoom, utan att behöva programmera hela logiken bakom dessa funktioner. Istället kan programmeraren fokusera sitt arbete på de delarna som gör just den kartapplikationen unik. Arbetet är uppdelat i en undersökande del för att klarlägga var utvecklingen av tekniken befinner sig idag och vilka liknande försök som gjorts tidigare och en mer praktisk utvecklingsdel med målet att implementera ett API för kartapplikationer på Android. I undersökningen jämförs Android med andra mobila plattformar, t.ex. Apples iPhone och Nokias Symbian. Det konstateras att Android står sig bra i konkurens med de andra och lämpar sig väl för kartapplikationer men att det skulle behövas ett generellt kartverktyg som inte är så hårt styrt som Google maps, som är det vanligaste kartverktyget för Android. För att tydliggöra vad API:et borde innehålla och klara av att utföra gjordes först en teoretisk modell av dess olika delar. De viktigaste delarna, t.ex. dataladdning och användargränssnitt med kartbildsvisning, panorering och zoom, implementerades sedan för att kunna testköras och vidareutvecklas på en Android-mobil. En demoapplikation utvecklades för att demonstrera användningen av API:et. Resultatet är ett verktyg för ett energibolags servicepersonal att ha med sig i fält för att se deras fjärrvärmenäts geografiska utsträckning och info om nätets olika delar, kopplingar och kunder.Scientific summary: The fast development of computational power of the mobile phone have made it a suitable platform for running map applications. Both public and field working professionals can benefit from easy access to a mobile map client application with features such as route planning, location based services and simple GIS operations. This master's thesis describes the mobile operating system (OS) Android from a geographic information aspect and relates it to other major mobile OS. A map client application programming interfaces (API) is implemented, resulting in a good performing map client. Though it needs additional development to perform all features aimed for in the suggested API design. The study is divided into a state-of-the-art investigation of available technology, and an effort to design and implement a map client API for Android. The investigation was made by referencing available scientific papers, technical articles and websites. Available OS's and API's are investigated. It is concluded that Android is a good platform choice for implementing mobile map applications. But there is need of a generic open source API for Android. Another objective of the study was to compare a map client running as a web application to the native client developed regarding performance. Unfortunately no suiting API for setting up the web application was found. Since then the OpenLayers community have made a great effort for running OpenLayers clients on mobile devices, which would have been an ideal choice for doing the comparison. The work on the API contains a theoretical model which is partly implemented. The aim of the model is to define the overall functionality, some specialized features and cohesive data structures. Then the base functionality, such as data loading, map drawing, panning and zooming, was implemented. The implementation was carried out in an iterative manner. Starting with complementing a basic, incomplete open source map API to gain understanding of mobile map API design and avoid re-inventing the wheel. Added was support for coordinate systems and projections other than WGS 84 Web Mercator (EPSG 4326), better Web Map Service (WMS) support, vector data loading and improved responsiveness when loading data. A demo application was put together in order to test performance on the hardware emulator integrated in the Android SDK and on a real device, Motorola Milestone running Android version 2.1. The scenario for the demo application is a district heating pipe system, an useful field application for a city energy company. The application shows a raster background map loaded from a tiled WMS with the pipe system as vector overlays loaded from a custom Keyhole Markup Language (KML) service. The vector data is click-able in order to show information about different parts of the pipe system

A comparison of two physical data designs for interactive social networking actions

This paper compares the performance of an SQL solution that implements a relational data model with a document store named MongoDB. We report on the performance of a single node configuration of each data store and assume the database is small enough to fit in main memory. We analyze utilization of the CPU cores and the network bandwidth to compare the two data stores. Our key findings are as follows. First, for those social networking actions that read and write a small amount of data, the join operator of the SQL solution is not slower than the JSON representation of MongoDB. Second, with a mix of actions, the SQL solution provides either the same performance as MongoDB or outperforms it by 20%. Third, a middle-tier cache enhances the performance of both data stores as query result look up is significantly faster than query processing with either system.

Towards Efficient Delivery of Dynamic Web Content

Advantages of cache cooperation on edge cache networks serving dynamic web content were studied. Design of cooperative edge cache grid a large-scale cooperative edge cache network for delivering highly dynamic web content with varying server update frequencies was presented. A cache clouds-based architecture was proposed to promote low-cost cache cooperation in cooperative edge cache grid. An Internet landmarks-based scheme, called selective landmarks-based server-distance sensitive clustering scheme, for grouping edge caches into cooperative clouds was presented. Dynamic hashing technique for efficient, load-balanced, and reliable documents lookups and updates was presented. Utility-based scheme for cooperative document placement in cache clouds was proposed. The proposed architecture and techniques were evaluated through trace-based simulations using both real-world and synthetic traces. Results showed that the proposed techniques provide significant performance benefits. A framework for automatically detecting cache-effective fragments in dynamic web pages was presented. Two types of fragments in web pages, namely, shared fragments and lifetime-personalization fragments were identified and formally defined. A hierarchical fragment-aware web page model called the augmented-fragment tree model was proposed. An efficient algorithm to detect maximal fragments that are shared among multiple documents was proposed. A practical algorithm for detecting fragments based on their lifetime and personalization characteristics was designed. The proposed framework and algorithms were evaluated through experiments on real web sites. The effect of adopting the detected fragments on web-caches and origin-servers is experimentally studied.Ph.D.Committee Chair: Dr. Ling Liu; Committee Member: Dr. Arun Iyengar; Committee Member: Dr. Calton Pu; Committee Member: Dr. H. Venkateswaran; Committee Member: Dr. Mustaque Ahama

CHORUS Deliverable 2.1: State of the Art on Multimedia Search Engines

Based on the information provided by European projects and national initiatives related to multimedia search as well as domains experts that participated in the CHORUS Think-thanks and workshops, this document reports on the state of the art related to multimedia content search from, a technical, and socio-economic perspective. The technical perspective includes an up to date view on content based indexing and retrieval technologies, multimedia search in the context of mobile devices and peer-to-peer networks, and an overview of current evaluation and benchmark inititiatives to measure the performance of multimedia search engines. From a socio-economic perspective we inventorize the impact and legal consequences of these technical advances and point out future directions of research

Federated Learning in Intelligent Transportation Systems: Recent Applications and Open Problems

Intelligent transportation systems (ITSs) have been fueled by the rapid development of communication technologies, sensor technologies, and the Internet of Things (IoT). Nonetheless, due to the dynamic characteristics of the vehicle networks, it is rather challenging to make timely and accurate decisions of vehicle behaviors. Moreover, in the presence of mobile wireless communications, the privacy and security of vehicle information are at constant risk. In this context, a new paradigm is urgently needed for various applications in dynamic vehicle environments. As a distributed machine learning technology, federated learning (FL) has received extensive attention due to its outstanding privacy protection properties and easy scalability. We conduct a comprehensive survey of the latest developments in FL for ITS. Specifically, we initially research the prevalent challenges in ITS and elucidate the motivations for applying FL from various perspectives. Subsequently, we review existing deployments of FL in ITS across various scenarios, and discuss specific potential issues in object recognition, traffic management, and service providing scenarios. Furthermore, we conduct a further analysis of the new challenges introduced by FL deployment and the inherent limitations that FL alone cannot fully address, including uneven data distribution, limited storage and computing power, and potential privacy and security concerns. We then examine the existing collaborative technologies that can help mitigate these challenges. Lastly, we discuss the open challenges that remain to be addressed in applying FL in ITS and propose several future research directions